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The Corn Rootworm Scouting Tips You Need to Know

September 6, 2019
An adult corn rootworm sitting on a leaf.

Look for adult corn rootworm beetles that can emerge as corn is silking.

Don’t underestimate western and northern corn rootworm (CRW), 2 highly adaptable and persistent pests in corn. Together, they’re known as the $1 Billion Pest because of the damage they can do to growers’ bottom-lines.

This year, the emergence of adult CRW beetles coincided with corn silking in many Midwestern locations. Beetles can clip silks, which hinders pollination and interferes with kernel growth.

Don’t let this pest eat away your profits. Now is an ideal time to scout your fields for CRW activity. Iowa State University Extension and Outreach recommends the following best practices to monitor for adults:

  1. As corn silking begins, set up yellow sticky traps (unbaited). Continue through the dent stage.
  2. Create 2 transects, with 6 sticky traps per transect, for every 10 to 50 acres of crop.
  3. The first trap should be at least 165’ from the field edge. Space the others in the same row, at 165’ apart.
  4. Attach the sticky trap directly to the growing corn ear.
  5. Perform weekly checks to see how many western and northern corn rootworm beetles have been caught. Then replace the traps.
  6. Calculate the average number of beetles per trap, per day using the formula:
    A math equation showing how to calculate the average number of corn rootworms in a field. The equation is as follows: Take the total number of corn rootworms found in field traps and divide by the number of traps. Take the quotient and divide by 7 to get the average number of corn rootworm per trap, per day.
  7. Know the action thresholds for CRW activity in your crop. For corn, it’s an average of 2 CRWs per trap, per day.
  8. If the threshold is met, consider crop rotation. If you’re planting corn again next season, use a pyramided Bt trait or soil-applied insecticide on non-rootworm Bt corn.

For corn growers, we recommend Force® 6.5G insecticide, which features a high-load granular formulation to give you proven control with fewer stops to refill. It manages CRW and other soil-dwelling insects with enhanced convenience.

Learn more about corn rootworm, what to look for and how to control it with the new Force 6.5G Interactive Infographic.

Are you seeing corn rootworm activity in your fields right now?
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September 4, 2019 - July 15, 2020
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While the weather this season may reduce next year’s corn rootworm population in some areas, other locations could see increased CRW numbers. Read our previous post to learn why a wet 2019 won’t stop 2020 insect pressure.

If a corn rootworm population is allowed to infest your fields, it could damage your crops, season after season. We have information to help you control the corn rootworm life cycle from the start.

Don’t miss the rest of our Know More, Grow More series on protecting your corn yields from insect pests.

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